Process for making low-density polyolefins

ABSTRACT

A process for making ethylene copolymers is disclosed. Ethylene copolymerizes with an α-olefin in the presence of a catalyst system comprising an activator and a silica-supported, bridged indenoindolyl metal complex having “open architecture.” The supported complex incorporates comonomers with exceptional efficiency, and the process gives ethylene copolymers having high molecular weights (Mw&gt;100K) and very low densities (&lt;0.910 g/cm 3 ). Open architecture catalysts that include bridging through the indolyl nitrogen of the indenoindolyl framework are also described.

FIELD OF THE INVENTION

The invention relates to a process for making polyolefins. The process, which uses catalysts having a bridged indenoindolyl ligand with “open architecture,” is valuable for making polyolefins with exceptionally low densities.

BACKGROUND OF THE INVENTION

While Ziegler-Natta catalysts are a mainstay for polyolefin manufacture, single-site (metallocene and non-metallocene) catalysts represent the industry's future. These catalysts are often more reactive than Ziegler-Natta catalysts, and they produce polymers with improved physical properties. The improved properties include narrow molecular weight distribution, reduced low molecular weight extractables, enhanced incorporation of α-olefin comonomers, lower polymer density, controlled content and distribution of long-chain branching, and modified melt rheology and relaxation characteristics.

Single-site olefin polymerization catalysts having “open architecture” are generally known. Examples include the so-called “constrained geometry” catalysts developed by scientists at Dow Chemical Company (see, e.g., U.S. Pat. No. 5,064,802), which have been used to produce a variety of polyolefins. “Open architecture” catalysts differ structurally from ordinary bridged metallocenes, which have a bridged pair of pi-electron donors. In open architecture catalysts, only one group of the bridged ligand donates pi electrons to the metal; the other group is sigma bonded to the metal. An advantage of this type of bridging is thought to be a more open or exposed locus for olefin complexation and chain propagation when the complex becomes catalytically active. Simple examples of complexes with open architecture are tert-butylamido(cyclopentadienyl)dimethyl-silylzirconium dichloride and methylamido(cyclopentadienyl)-1,2-ethanediyltitanium dimethyl:

Organometallic complexes that incorporate “indenoindolyl” ligands are known (see U.S. Pat. No. 6,232,260 and PCT Int. Appl. WO 99/24446 (“Nifant'ev”)). The '260 patent demonstrates the use of non-bridged bis(indenoindolyl) complexes for making HDPE in a slurry polymerization. Versatility is an advantage of the complexes; by modifying the starting materials, a wide variety of indenoindolyl complexes can be prepared. “Open architecture” complexes are neither prepared nor specifically discussed. Nifant'ev teaches the use of bridged indenoindolyl complexes as catalysts for making polyolefins, including polypropylene, HDPE and LLDPE. The complexes disclosed by Nifant'ev do not have open architecture.

PCT Int. Appl. WO 01/53360 (Resconi et al.) discloses bridged indenoindolyl complexes having open architecture and their use to produce substantially amorphous propylene-based polymers. Resconi teaches many open architecture complexes but none that are bridged through the indolyl nitrogen. Moreover, all of the complexes are used only to make propylene polymers; their use to produce low-density ethylene polymers is not disclosed.

As noted earlier, the indenoindolyl framework is versatile. The need continues, however, for new ways to make polyolefins—especially ethylene copolymers—with very low densities. In particular, it is difficult to make ethylene polymers having densities less than about 0.915 g/cm³ using known indenoindolyl complexes. On the other hand, ethylene polymers having such low densities are valuable for special applications requiring elastomeric properties. The industry would also benefit from the availability of new catalysts that capitalize on the inherent flexibility of the indenoindolyl framework.

SUMMARY OF THE INVENTION

The invention is a process for making ethylene copolymers. The process comprises copolymerizing ethylene with an α-olefin in the presence of a catalyst system comprising an activator and a silica-supported organometallic complex. The complex, which has “open architecture,” includes a Group 4 to 6 transition metal and a bridged indenoindolyl ligand. Because the supported complex incorporates comonomers with exceptional efficiency, the process enables the production of ethylene copolymers having high molecular weights (Mw>100K) and very low densities (<0.910 g/cm ³). The invention includes new open architecture catalysts that take advantage of bridging through the indolyl nitrogen of the indenoindolyl framework.

DETAILED DESCRIPTION OF THE INVENTION

In the process of the invention, ethylene polymerizes with one or more α-olefins to give a copolymer having very low density. Suitable α-olefins are 1-butene, 1-hexene, 1-octene, and mixtures thereof. 1-Hexene is particularly preferred.

Catalyst systems useful for the process comprise an activator and a silica-supported, indenoindolyl Group 4-6 transition metal complex having open architecture. More preferred complexes include a Group 4 transition metal such as titanium or zirconium.

“Indenoindolyl” ligands are generated by deprotonating an indenoindole compound using a potent base. By “indenoindole compound,” we mean an organic compound that has both indole and indene rings. The five-membered rings from each are fused, i.e., they share two carbon atoms. Preferably, the rings are fused such that the indole nitrogen and the only sp³-hybridized carbon on the indenyl ring are “trans” to each other. Such is the case in an indeno[1,2-b] ring system such as:

Suitable ring systems also include those in which the indole nitrogen and the sp³-hybridized carbon of the indene are beta to each other, i.e., they are on the same side of the molecule. This is an indeno[2,1-b]indole ring system:

The ring atoms can be unsubstituted or substituted with one or more groups such as alkyl, aryl, aralkyl, halogen, silyl, nitro, dialkylamino, diarylamino, alkoxy, aryloxy, thioether, or the like. Additional fused rings can be present, as long as an indenoindole moiety is present.

Numbering of indenoindoles follows IUPAC Rule A-22. The molecule is oriented as shown below, and numbering is done clockwise beginning with the ring at the uppermost right of the structure in a manner effective to give the lowest possible number to the heteroatom. Thus, 5,10-dihydroindeno[1,2-b]indole is numbered as follows:

while 5,6-dihydroindeno[2,1-b]indole has the numbering:

For correct nomenclature and numbering of these ring systems, see the Ring Systems Handbook (1998), a publication of Chemical Abstracts Service, Ring Systems File II: RF 33986-RF 66391 at RF 58952 and 58955. (Other examples of correct numbering appear in PCT Int. Appl. WO 99/24446.)

Methods for making indenoindole compounds are well known. Suitable methods and compounds are disclosed, for example, in U.S. Pat. No. 6,232,260, the teachings of which are incorporated herein by reference, and references cited therein, including the method of Buu-Hoi and Xuong, J. Chem. Soc. (1952) 2225. Suitable procedures also appear in PCT Int. Appls. WO 99/24446 and WO 01/53360.

Indenoindolyl complexes useful for the process of the invention have open architecture. By “open architecture,” we mean a complex having a fixed geometry that enables generation of a highly exposed active site when the catalyst is combined with an activator. The metal of the complex is pi-bonded to the indenyl Cp ring and is also sigma-bonded through two or more atoms to the indolyl nitrogen or the indenyl methylene carbon. (In contrast, many of the bridged indenoindolyl complexes described in the literature have a transition metal that is pi-bonded to the indenyl Cp ring and pi-bonded to another Cp-like group. See, e.g., U.S. Pat. No. 6,232,260 or WO 99/24446). Preferably, the metal is sigma-bonded to a heteroatom, i.e., oxygen, nitrogen, phosphorus, or sulfur; most preferably, the metal is sigma-bonded to nitrogen. The heteroatom is linked to the indenoindolyl group through a bridging group, which is preferably dialkylsilyl, diarylsilyl, methylene, ethylene, isopropylidene, diphenylmethylene, or the like. Particularly preferred bridging groups are dimethylsilyl, methylene, ethylene, and isopropylidene. The bridging group is covalently bonded to either the indolyl nitrogen atom or the indenyl methylene carbon.

In addition to the bridged indenoindolyl ligand, the organometallic complex usually includes one or more labile anionic ligands such as halides, alkoxys, aryloxys, alkyls, alkaryls, aryls, dialkylaminos, or the like. Particularly preferred are halides, alkyls, and alkaryls (e.g., chloride, methyl, benzyl).

In a preferred process of the invention, the indenoindolyl complex has the general structure:

in which M is a Group 4-6 transition metal, G is a linking group, L is a ligand that is covalently bonded to G and M, R is alkyl, aryl, or trialkylsilyl, X is alkyl, aryl, alkoxy, aryloxy, halide, dialkylamino, or siloxy, and n satisfies the valence of M. More preferably, M is a Group 4 transition metal, L is alkylamido, G is dialkylsilyl, and X is halide or alkyl.

In another preferred process, the indenoindolyl complex has the general structure:

in which M is a Group 4-6 transition metal, G is a linking group, L is a ligand that is covalently bonded to G and M, X is alkyl, aryl, alkoxy, aryloxy, halide, dialkylamino, or siloxy, and n satisfies the valence of M. Preferably, M is a Group 4 transition metal, L is alkylamido, G is dialkylsilyl, and X is halide or alkyl.

Exemplary organometallic complexes useful for the process of the invention:

The complexes can be made by any suitable method; those skilled in the art will recognize a variety of acceptable synthetic strategies. See especially PCT Int. Appl. WO 01/53360 for suitable routes. Often, the synthesis begins with preparation of the desired indenoindole compound from particular indanone and arylhydrazine precursors. In one convenient approach, the indenoindole is deprotonated and reacted with dichlorodimethylsilane to attach a chlorodimethylsilyl group to the indenyl methylene carbon. Subsequent reaction with an amine or, more preferably, an alkali metal amide compound such as lithium tert-butylamide (from tert-butylamine and n-butyllithium), displaces chloride and gives the desired silylamine product. Double deprotonation and reaction with a transition metal source gives the target indenoindolyl metal complex having open architecture. A typical reaction sequence follows:

A similar complex can be generated by amine elimination, which may or may not require heating, with a method explored by Professor Richard F. Jordan and coworkers at the University of Iowa:

For additional examples of this approach to making organometallic complexes, see U.S. Pat. No. 5,495,035; J. Am. Chem. Soc. 118 (1996) 8024; and Organometallics 15 (1996) 4045.

The process of the invention can also utilize complexes in which bridging to the indenoindolyl group occurs through the indolyl nitrogen atom. A convenient route to an N-Si-N bridged complex is shown below:

Or with amine elimination to form a similar complex:

Similar strategies can be used to make a wide variety of indenoindolyl metal complexes having open architecture.

Any convenient source of the transition metal can be used to make the complex. As shown above, the transition metal source conveniently has labile ligands such as halide or dialkylamino groups that can be easily replaced by the indenoindolyl and amido anions of the bridged indenoindolyl ligand. Examples are halides (e.g., TiCl₄, ZrCl₄), alkoxides, amides, and the like.

Catalyst systems useful in the process include, in addition to the indenoindolyl metal complex, an activator. The activator helps to ionize the organometallic complex and activate the catalyst. Suitable activators are well known in the art. Examples include alumoxanes (methyl alumoxane (MAO), PMAO, ethyl alumoxane, diisobutyl alumoxane), alkylaluminum compounds (triethylaluminum, diethyl aluminum chloride, trimethylaluminum, triisobutyl aluminum), and the like. Suitable activators include acid salts that contain non-nucleophilic anions. These compounds generally consist of bulky ligands attached to boron or aluminum. Examples include lithium tetrakis(pentafluorophenyl)borate, lithium tetrakis(pentafluorophenyl)aluminate, anilinium tetrakis(penta-fluorophenyl)borate, and the like. Suitable activators also include organoboranes, which include boron and one or more alkyl, aryl, or aralkyl groups. Suitable activators include substituted and unsubstituted trialkyl and triarylboranes such as tris(pentafluorophenyl)borane, triphenylborane, tri-n-octylborane, and the like. These and other suitable boron-containing activators are described in U.S. Pat. Nos. 5,153,157, 5,198,401, and 5,241,025, the teachings of which are incorporated herein by reference. Suitable activators also include aluminoboronates—reaction products of alkyl aluminum compounds and organoboronic acids—as described in U.S. Pat. Nos. 5,414,180 and 5,648,440, the teachings of which are incorporated herein by reference. Alumoxane activators, such as MAO, are preferred.

The optimum amount of activator needed relative to the amount of organometallic complex depends on many factors, including the nature of the complex and activator, the desired reaction rate, the kind of polyolefin product, the reaction conditions, and other factors. Generally, however, when the activator is an alumoxane or an alkyl aluminum compound, the amount used will be within the range of about 0.01 to about 5000 moles, preferably from about 10 to about 500 moles, and more preferably from about 10 to about 200 moles, of aluminum per mole of transition metal, M. When the activator is an organoborane or an ionic borate or aluminate, the amount used will be within the range of about 0.01 to about 5000 moles, preferably from about 0.1 to about 500 moles, of activator per mole of M. The activator can be combined with the complex and added to the reactor as a mixture, or the components can be added to the reactor separately.

The process uses a silica-supported catalyst system. The silica is preferably treated thermally, chemically, or both prior to use to reduce the concentration of surface hydroxyl groups. Thermal treatment consists of heating (or “calcining”) the silica in a dry atmosphere at elevated temperature, preferably greater than about 100° C., and more preferably from about 150 to about 600° C., prior to use. A variety of different chemical treatments can be used, including reaction with organo-aluminum, -magnesium, -silicon, or -boron compounds. See, for example, the techniques described in U.S. Pat. No. 6,211,311, the teachings of which are incorporated herein by reference.

While there are many ways to practice the ethylene copolymerization process of the invention, the process is preferably a slurry or gas-phase process. These processes are well-suited to the use of supported catalysts. Suitable methods for polymerizing olefins using the catalysts of the invention are described, for example, in U.S. Pat. Nos. 5,902,866, 5,637,659, and 5,539,124, the teachings of which are incorporated herein by reference.

The polymerizations can be performed over a wide temperature range, such as about −30° C. to about 280° C. A more preferred range is from about 30° C. to about 180° C.; most preferred is the range from about 60° C. to about 100° C. Olefin partial pressures normally range from about 15 psia to about 50,000 psia. More preferred is the range from about 15 psia to about 1000 psia.

Catalyst concentrations used for the olefin polymerization depend on many factors. Preferably, however, the concentration ranges from about 0.01 micromoles per liter to about 100 micromoles per liter. Polymerization times depend on the type of process, the catalyst concentration, and other factors. Generally, polymerizations are complete within several seconds to several hours.

The invention includes a catalyst system. The catalyst system comprises an activator, as described above, and a bridged indenoindolyl Group 4-6 transition metal complex. The complex has an open architecture in which bridging to the indenoindolyl group occurs through the indolyl nitrogen. The complexes are produced as described earlier. In preferred catalyst systems of the invention, the indenoindolyl complex has the general structure:

in which M is a Group 4-6 transition metal, G is a linking group, L is a ligand that is covalently bonded to G and M, X is alkyl, aryl, alkoxy, aryloxy, halide, dialkylamino, or siloxy, and n satisfies the valence of M. Preferably, M is a Group 4 transition metal, L is alkylamido, G is dialkylsilyl, and X is halide or alkyl.

Exemplary indenoindolyl complexes for catalyst systems of the invention:

The invention enables the preparation of ethylene copolymers having very low densities. Generally, the copolymers can have densities less than about 0.930 g/cm³. An advantage of the invention, however, is the ability to depress densities to much lower values, i.e., less than 0.910 g/cm³, and even less than 0.890 g/cm³. As shown in Table 1, achieving very low densities is difficult for indenoindolyl metal catalysts that lack an open architecture (see Comparative Examples 2 and 3). We found that an open architecture catalyst incorporates comonomers more efficiently (see Example 1).

The catalyst system and process of the invention can be used to produce ethylene polymers having high molecular weights. For example, very low density polyolefins having weight average molecular weights (Mw) greater than 400,000, or even greater than 1,000,000, can be easily produced (see Example 4). When desirable, hydrogen or other chain-transfer agents can be introduced into the reactor to regulate polymer molecular weight.

Polyolefins produced by the process of the invention usually have narrow molecular weight distributions, preferably less than about 3.5, more preferably less than about 3.0. When a comonomer is included, a high level of short-chain branching is evident by FT-IR analysis. When the goal is to make polyolefins with very low density, the copolymers have more then about 20, preferably more than about 30, branches per 1000 carbons.

The following examples merely illustrate the invention. Those skilled in the art will recognize many variations that are within the spirit of the invention and scope of the claims.

PREPARATION OF COMPLEX A Open Architecture Complex 4

(a) Preparation of Indeno[1,2-b]indole 1. A mixture of 1-indanone (30.6 g, 232 mmol) and p-tolylhydrazine hydrochloride (37.0 g, 233 mmol) in EtOH (350 mL) and aqueous HCl (12 N, 18 mL) are heated to reflux for 90 min. The mixture is cooled and filtered, and the solid is washed with EtOH (600 mL) followed by 20% aqueous EtOH (400 mL) and finally hexanes (200 mL). The off-white solid is dried under vacuum (36.5 g, 72%).

(b) N-Methylation of 1. A mixture of 1 (36.5 g, 166 mmol), aqueous NaOH solution (112 mL, 20 M, 2.2 mol), C₁₆H₃₃NMe₃Br (0.65 g, 1.78 mmol), and toluene (112 mL) is vigorously stirred at room temperature. A solution of Mel (17.0 mL, 273 mmol) in toluene (15 mL) is added dropwise, and the mixture is stirred at room temperature for 4 h and refluxed for 3 h. A crystalline solid forms upon cooling and is filtered and washed with cold (−78° C.) EtOH (300 mL) followed by hexanes (100 mL). The layers are separated and the aqueous fraction is washed with toluene (2×100 mL). The organics are combined and dried over Na₂SO₄ and filtered. The volatiles are removed under vacuum and the precipitate is dried and combined with the crystalline product 2 (total yield 25.7 g, 66%).

(c) Bridged ligand preparation (3). n-Butyllithium (8 mL, 2.5 M in hexane, 20 mmol) is added dropwise to a solution of 2 (4.66 g, 21 mmol) in dry ether (70 mL). After 2 h, this solution is slowly added to a solution of dichlorodimethylsilane (5.20 g) in ether (30 mL). After 2 h of stirring at room temperature, the mixture is filtered and evaporated. The residue is redissolved in ether (60 mL), and an ethereal solution of lithium t-butylamide (prepared in the usual manner from t-butylamine (1.46 g) and n-butyllithium (8 mL of 2.5 M solution)) is added dropwise. The mixture is stirred for 3 h, and is then filtered through Celite filter aid. After concentrating the filtrate, the residue is collected with pentane and chilled to −30° C. Yield of bridged ligand 3: 6 g (82%).

(d) Preparation of open architecture complex 4. Bridged ligand 3 (6 g) is dissolved in ether (120 mL) and n-butyllithium (13.5 mL of 2.5 M solution in hexane) is added. After stirring overnight at room temperature, methyllithium (24.5 mL of 1.4 M solution in ether) is added, and the mixture is cooled to −30° C. Titanium tetrachloride bis(tetrahydrofuran) complex (5.66 g) is added, and stirring continues for 3 h. The mixture is filtered and the filtrate is concentrated. The residue is extracted with hot heptane (2×100 mL). The combined filtrates are evaporated, and the residue is crystallized with pentane and cooled to −30° C. The product, complex 4, is a dark brown solid. Yield: 4.67 g.

The ¹H NMR spectrum is consistent with the proposed structure:

PREPARATION OF COMPLEX B —COMPARATIVE EXAMPLE Bridged Indeno[2,1-b]indolylzirconium Complex 9

(a) Preparation of Indeno[2,1-b]indole 5. A mixture of 2-indanone (51.0 g, 0.39 mol) and p-tolylhydrazine hydrochloride (61.4 g, 0.39 mol) is dissolved in glacial acetic acid (525 mL) and is vigorously stirred and heated to reflux. The mixture turns red and is heated for 2 h. After cooling to room temperature, it is poured into ice water (1 L). The precipitate is filtered to afford a solid, which is washed with water (about 1 L). The solid is dissolved in ethyl acetate (1.4 L), activated charcoal is added, and the mixture is gently warmed. The mixture is then cooled and filtered over a pad of Celite. The filtrate is dried over Na₂SO₄, filtered, and is then concentrated to 450 mL and cooled to −30° C. for 3 days. The crystalline solid is filtered and washed with chilled (−78° C.) hexanes (2×500 mL). The beige solid is collected and dried under vacuum (47.1 g, 56%).

(b) N-Methylation of 5 to give 6. A slurry of aqueous NaOH (42 mL, 21.5 M, 903 mmol), C₁₆H₃₃NMe₃Br (0.36 g, 0.97 mmol), and 5 (15.0 g, 68.4 mmol) is combined with toluene (50 mL). A solution of Mel (8.0 mL, 129 mmol) in toluene (15 mL) is added dropwise at room temperature. The mixture is stirred at room temperature for 2.5 h and then refluxed for an hour. The mixture turns red and is cooled to room temperature and filtered. The crystalline solid is washed with chilled (−30° C.) EtOH (200 mL) followed by chilled hexanes (200 mL) to afford a pale red solid (10.3 g, 65%).

(c) Anion generation: Preparation of 7. n-Butyllithium (13.0 mL, 2.5 M in hexanes, 32.5 mmol) is added at room temperature to a slurry of 6 (4.94 g, 21.1 mmol) in toluene (125 mL). The mixture is maintained at room temperature and turns pale yellow. A precipitate forms after 2 h. After 2 days, the mixture is filtered to give a pale beige solid. The solid is washed with toluene (60 mL), followed by hexanes (30 mL), and is then collected and dried under vacuum (4.37 g, 87%).

(d) Preparation of Dianion 8. Product 7 (4.57 g, 19.1 mmol) is suspended in toluene (100 mL). Diethyl ether (40 mL) is added dropwise to afford an orange solution, which is added to a solution of SiCl₂Me₂ (12.0 mL, 98.9 mmol) in Et₂O (100 mL) at room temperature.. The mixture turns cloudy and dirty beige and is stirred for 3 days and filtered to give a dark red-orange solution. Volatiles are removed under reduced pressure to afford an oily solid. An aliquot is analyzed by ¹H NMR, revealing is formation of the desired product; 100% conversion is presumed. The oily solid is dissolved in Et₂O (140 mL), and NaCp (11.0 mL, 2.0 M in THF, 22 mmol) is added. A precipitate forms immediately, and stirring continues for 2 days. The mixture is washed with water (3×50 mL), and the organic phase is dried over Na₂SO₄ and filtered. Volatiles are removed under vacuum to give an oily residue, and 100% conversion is assumed. The residue was dissolved in Et₂O (75 mL) and cooled to −78° C. n-Butyllithium (18.0 mL, 2.5 M in hexanes, 45.0 mmol) is added by syringe, and the mixture is warmed to room temperature slowly. A yellow solid precipitates overnight, and volatiles are removed under vacuum. The crude material is washed with hexanes (100 mL) and filtered to afford a yellow powder. The powder is collected and dried under vacuum (6.73 g, 93%).

(e) Preparation of Complex 9. Zirconium tetrachloride (3.15 g, 13.5 mmol) is combined with toluene (100 mL) and dissolved in Et₂O (50 mL) to produce a cloudy suspension. Dianion 8 (5.02 g, 13.7 mmol) is added as a solid in portions over the course of 30 min. The color turns from yellow to dark orange, and a precipitate forms. The mixture is maintained at room temperature for 2 days and is filtered to give a dirty yellow solid. The solid is washed with toluene (50 mL) and hexanes (50 mL). The yellow powder is collected and dried under vacuum (3.72 g, 53%).

The ¹H NMR spectrum is consistent with the proposed structure:

PREPARATION OF COMPLEX C—Comparative Example Unbridged Indeno[1,2-b]indolylzirconium Complex 10

In a glovebox under nitrogen, N-methylated indeno[1,2-b]indole 2 (14.2 g, 60.9 mmol), prepared as described earlier, is dissolved in toluene (175 mL). n-Butyllithium (38.0 mL of 2.5 M solution in hexanes, 95 mmol) is added carefully under vigorous stirring at room temperature to give a red solution. After one hour, a precipitate forms. The mixture is kept at room temperature overnight, and is then filtered and washed with toluene (100 mL) and then heptane (200 mL). The sticky product is dried under nitrogen in the glovebox and is collected and dried under vacuum.

A sample of the indeno[1 2-b]indolyl lithium salt produced above (10 g, 42 mmol) is dissolved in toluene (95 mL) to produce an orange slurry. Diethyl ether (35 mL) is added slowly to give an orange solution. This solution is added over 15 min. at room temperature with stirring to a slurry of cyclopentadienylzirconium trichloride (11 g, 42 mmol) in toluene (190 mL) and diethyl ether (190 mL). The mixture turns deep red and is kept at room temperature overnight. The slurry is filtered to recover a red solid, which is washed with toluene (200 mL) and dried under vacuum. Yield of complex 10: 16.5 g. The ¹H NMR spectrum is consistent with the proposed structure:

Preparation of Silica-Supported Complexes

Crossfield ES757 silica is calcined at 250° C. for 12 h. In a glove-box under nitrogen, a 30 wt. % solution of methylalumoxane (MAO) in toluene (0.8 mL) is slowly added to a sample (1.0 g) of the calcined silica at room temperature with efficient stirring. After the MAO addition is complete, stirring continues for 0.5 h. Volatiles are removed under vacuum (about 28.5 inches Hg, 1 hour) at room temperature. Yield:1.25 g of MAO-treated silica.

Also in the glovebox, 30 wt. % MAO/toluene solution (1.18 mL) is added to an amount of organometallic complex (A, B, or C) equal to 0.11 mmol of transition metal. The resulting solution is added slowly at room temperature with stirring to the dry, MAO-treated silica described above. After stirring for an additional 0.5 h, the supported complex is dried under vacuum to give a supported complex (about 1.75 g).

EXAMPLE 1 AND COMPARATIVE EXAMPLES 2-3 Copolymerization of Ethylene and 1-Hexene

A one-liter, stainless-steel reactor is charged with 1-hexene (35 mL). Triisobutylaluminum (1.0 mL of 1.0 M solution in heptane, 1.0 mmol) and Armostat® 710 fatty amine (1 mg, product of Akzo Nobel) in heptane solution (0.25 mL) are mixed in one sidearm of the injector. This mixture is then flushed into the reactor with nitrogen pressure and isobutane (about 450 mL). Hydrogen is added (10 dpsig from a 90-mL stainless-steel cylinder pressurized initially to 500 psig H₂) to the reactor, which is then pressurized with ethylene to 320 psig. The reactor contents are allowed to equilibrate at 80° C. The supported catalyst (30 mg) is loaded into the other injector arm and then flushed into the reactor with isobutane (100 mL) and nitrogen pressure. The polymerization proceeds for 0.5 h. The reactor is vented and the olefin polymer is collected and dried under vacuum at 60° C. prior to testing. Results of polymer testing appear in Table 1.

TABLE 1 Effect of Open Architecture on Polymer Density density Ex. Complex Type SCB (g/cm³) Mw Mw/Mn 1 A open architecture Ti 30.3 0.889 784 K 3.0 [1, 2-b] complex C2 B bridged Zr 17.0 0.913 100 K 3.1 [2, 1-b] complex C3 C unbridged Zr  6.2 0.932  94 K 2.8 [1, 2-b] complex SCB = short-chain branches per 1000 carbons as measured by FT-IR.

EXAMPLE 4 Copolymerization of Ethylene and 1-Hexene

A one-liter, stainless-steel reactor is charged with 1-hexene (35 mL). Triisobutylaluminum (0.20 mL of 1.0 M solution in heptane, 0.20 mmol) is flushed into the reactor from one sidearm of the injector with isobutane (450 mL) and nitrogen pressure. The reactor is then pressurized with ethylene to 320 psig. The reactor contents are allowed to equilibrate at 80° C. The supported catalyst (34 mg of silica-supported complex A) is loaded into the other injector arm and then flushed into the reactor with isobutane (100 mL) and nitrogen pressure. The polymerization proceeds for 0.5 h. The reactor is vented and the olefin polymer is collected and dried under vacuum at 60° C. prior to testing. Activity: 6120 g polyolefin per g catalyst per hour. Mw/Mn (GPC)=2.44. Mw=1,180,000; intrinsic viscosity (by GPC): 9.57; short-chain branches per 1000 carbons (by FT-IR): 32.8; density: 0.888 g/cm³.

Example 4 demonstrates the use of an open architecture indenoindolyl catalyst in a process of the invention for making ethylene copolymers. As shown in Table 1, the copolymers have very low densities, high molecular weight (even though hydrogen was present in the reactor), and narrow molecular weight distributions (2.8-3.0).

Preparation of Supported Catalyst D With Complex A and Borate Co-catalyst

Grace Davison silica 955 is calcined at 250° C. for 12 h. In a glove-box under nitrogen, a 0.5 M solution of triethylaluminum (TEAL) in heptane (8 mL) is slowly added to 2. g of the calcined silica at room temperature with efficient stirring. After one hour stirring, the treated silica is dried by vacuum at room temperature.

Complex A (29 mg, 0.066 mmol), toluene (5 mL), and triphenylcarbenium tetrakis(pentafluorophenyl)borate [(C₆H₅)₃CB(C₆F₅)₄](85 mg, 0.092 mmol) are mixed with a sample of the TEAL-treated silica (1.0 g) and the mixture is stirred for 0.5 h. Volatiles are removed under vacuum (about 28.5 inches Hg, 1 hour) at room temperature. Yield: 1.12 g of catalyst D.

EXAMPLE 5 Copolymerization of Ethylene and 1-Hexene

A one-liter, stainless-steel reactor is charged with 1-hexene (35 mL). Triisobutylaluminum (0.20 mL of 1.0 M solution in heptane, 0.20 mmol) is flushed into the reactor from one sidearm of the injector with isobutane (450 mL) and nitrogen pressure. The reactor is then pressurized with ethylene to 320 psig. The reactor contents are allowed to equilibrate at 80° C. Supported catalyst D (20 mg) is loaded into the other injector arm and is then flushed into the reactor with isobutane (100 mL) and nitrogen pressure. The polymerization proceeds for 0.5 h. The reactor is vented and the olefin polymer is collected and dried under vacuum at 60° C. prior to testing. Activity: 2680 g polyolefin per g catalyst per hour. Mw/Mn (GPC)=2.32. Mw=923,360; intrinsic viscosity (by GPC): 8.1; short-chain branches per 1000 carbons (by FT-IR): 33.2; density: 0.882 g/cm³.

Example 5 demonstrates the use of a borate-activated, open architecture indenoindolyl catalyst in a process of the invention for making ethylene copolymers with very low densities and high molecular weight.

EXAMPLE 6 Preparation of an N-Si-N Bridged Complex

2-Methyl-5,6-dihydroindeno[1,2-b]indole (3.28 g) is suspended in ether (30 mL) and n-butyllithium (6.0 mL of a 2.5 M solution in hexane) is added. After one hour, this mixture is added dropwise to a solution of dimethyldichlorosilane (4.14 g) in ether (20 mL). The mixture is stirred for three hours and filtered. The filtrate is evaporated to give a beige solid (4.68 g). The residue is dissolved in ether (60 mL), and a mixture of t-butylamine (1.20 g) and n-butyllithium (6.0 mL of a 2.5 M solution in hexane) is added dropwise. After 2 h, the mixture is evaporated and the residue is extracted with pentane. The volume of the mixture is reduced to 30 mL, and n-butyllithium (12 mL of 2.5 M solution in hexane) is added. After stirring overnight, the yellow solid is collected by filtration, washed with pentane, and dried. Yield: 4.49 g. The product is dissolved in ether (100 mL) and methyllithium (18 mL of a 1.4 M solution in ether) is added. The mixture is cooled to −30° C. and TiCl₄(THF)₂ (4.15 g) is then added. After stirring for 2 hours, the mixture is filtered and the filtrate is evaporated. The residue is extracted with hot heptane (2×100 mL). Evaporation of the combined extracts gives a brown-black solid (2.00 g) having a ¹H NMR spectrum consistent with the proposed structure:

EXAMPLE 7 Copolymerization Experiments

Ethylene is copolymerized with 1-hexene using an 8-cell Endeavor apparatus. Each cell is charged with a toluene solution containing 9.8×10⁻⁵ mmoles of the open-architecture Ti complex from Example 6, MAO activator (1000 equivalents) and varying amounts of 1-hexene comonomer. The apparatus is pressurized with ethylene (200 psig) and polymerizations proceed for 30 minutes. The gas is vented and polymer is collected from each of the cells. Activities are listed in Table 2.

TABLE 2 Ethylene-Hexene Copolymerizations 1-hexene (mL) 0 0.25 0.50 0.75 1.0 1.25 1.50 toluene (mL) 4.60 4.35 4.10 3.85 3.60 3.35 3.10 activity 26 22 19 17 13 11 3 (kg polymer per gram Ti per hour)

The preceding examples are meant only as illustrations. The following claims define the invention. 

We claim:
 1. A process which comprises copolymerizing ethylene with at least one α-olefin selected from the group consisting of 1-butene, 1-hexene, and 1-octene in the presence of a catalyst system which comprises an activator and a silica-supported, indenoindolyl Group 4-6 transition metal complex having open architecture to produce an ethylene copolymer having a density less than about 0.910 g/cm³.
 2. The process of claim 1 wherein the α-olefin is 1-hexene.
 3. The process of claim 1 wherein the activator is selected from the group consisting of alumoxanes, ionic borates, ionic aluminates, alkylaluminums, and aluminoboronates.
 4. The process of claim 1 wherein the complex incorporates a Group 4 transition metal.
 5. The process of claim 1 wherein the complex has the general structure:

in which M is a Group 4-6 transition metal, G is a linking group, L is a ligand that is covalently bonded to G and M, R is alkyl, aryl, or trialkylsilyl, X is alkyl, aryl, alkoxy, aryloxy, halide, dialkylamino, or siloxy, and n satisfies the valence of M.
 6. The process of claim 5 wherein M is a Group 4 transition metal, L is alkylamido, and G is dialkylsilyl.
 7. The process of claim 5 wherein M is Ti or Zr, L is t-butylamido, G is dimethylsilyl, and X is halide or alkyl.
 8. The process of claim 1 wherein the complex has the general structure:

in which M is a Group 4-6 transition metal, G is a linking group, L is a ligand that is covalently bonded to G and M, X is alkyl, aryl, alkoxy, aryloxy, halide, dialkylamino, or siloxy, and n satisfies the valence of M.
 9. The process of claim 8 wherein M is a Group 4 transition metal, L is alkylamido, and G is dialkylsilyl.
 10. The process of claim 8 wherein M is Ti or Zr, L is t-butylamido, G is dimethylsilyl, and X is halide or alkyl.
 11. The process of claim 1 wherein the silica support is pretreated with an alumoxane.
 12. The process of claim 1 wherein the ethylene copolymer has a Mw >400,000.
 13. The process of claim 1 wherein the ethylene copolymer has a density less than about 0.900 g/cm³.
 14. The process of claim 1 wherein the ethylene copolymer has a density less than about 0.890 g/cm³.
 15. The process of claim 1 wherein the ethylene copolymer has a Mw/Mn<3.0.
 16. The process of claim 1 wherein the ethylene copolymer has a Mw>1,000,000.
 17. A catalyst system which comprises: (a) an activator; and (b) a bridged indenoindolyl Group 4-6 transition metal complex having open architecture in which bridging to the indenoindolyl group occurs through the indolyl nitrogen.
 18. The catalyst system of claim 17 wherein the activator is selected from the group consisting of alumoxanes, ionic borates, ionic aluminates, alkylaluminums, and aluminoboronates.
 19. The catalyst system of claim 17 wherein the complex incorporates a Group 4 metal.
 20. The catalyst system of claim 17 wherein the complex has the general structure:

in which M is a Group 4-6 transition metal, G is a linking group, L is a ligand that is covalently bonded to G and M, X is alkyl, aryl, alkoxy, aryloxy, halide, dialkylamino, or siloxy, and n satisfies the valence of M.
 21. The catalyst system of claim 20 wherein M is Ti or Zr, L is t-butylamido, G is dialkylsilyl, and X is halide or alkyl. 